Shearography is an interferometric method which measures displacement derivatives. This paper presents a technique which eliminates the ambiguity in shearographic fringe interpretation. The technique is based on generating a carrier fringe pattern. Introduction of the carrier fringes results in the formation of a fringe pattern which has monotonically increasing fringe orders, thus allowing fringe orders to be determined in a straightforward manner and without ambiguity. The phase change due to deformation alone is then obtained by simply subtracting the known undeformed carrier fringe orders from the deformed carrier fringe orders. Elimination of fringe ambiguity has paved a way for automatic data acquisition in shearography. © 1988.
Hung, Y. Y., Hovanesian, J. D., & Takezaki, J. (1988). A fringe carrier technique for unambiguous determination of fringe orders in shearography. Optics and Lasers in Engineering, 8(2), 73–81. https://doi.org/10.1016/0143-8166(88)90044-9